In many integrated circuit designs, it is often desirable to provide a reference circuit for generating a known bias voltage or current. Reference circuits are generally either non-biased or self-biased. Non-biased circuits rely on discrete voltage drop devices (e.g., resistors or diodes) to arrive at the reference value. An example of a non-biased reference circuit may include a resistor divider, in which a string of resistors are connected together in series between a high voltage supply and a low voltage supply to generate the reference output. A disadvantage of the non-biased circuit is that the current drawn by the circuit is proportional to supply voltage, and that its reference value typically varies widely with the supply voltage level. Self-biased circuits rely on transistor biasing to generate an output reference value that is less sensitive to supply voltage variations. A disadvantage of the self-biased circuit is that the transistor device is susceptible to damage when used in a high-voltage supply application.
Often, the reference output is connected to an input/output (I/O) pad for making the reference voltage available externally. In this scenario, noise can be injected onto the reference output, which is undesirable. When a resistor divider is used to generate the reference output, sensitivity to noise can be reduced by increasing the current in the resistor string. However, this approach has a penalty of increasing power consumption in the reference circuit.